Organic light-emitting display device

ABSTRACT

The present invention provides OLEDs of the top emission type comprising organic light-emitting (LE) elements by preventing the problems such as the widening of the power lines, the reduction in the aperture ratio caused by the widening of the upper and the lower capacitor electrodes and the short circuit between the upper and the lower electrodes caused by the roughness of the flattening layers. Two kinds of the OLEDs are provided. One is an OLED comprising a region of LE layer sandwiched between the upper and lower electrodes is formed on a power line of TFT for driving the pixel. Another comprises a region of the LE layer formed on an electrode of capacitor connected to the TFTs to control the light-emitting element. Accordingly, without forming a flattening layer on the light-emitting layer, there is no electric short circuit between the lower electrode and the upper electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light-emitting displaydevice. More specifically, the present invention relates to an organiclight-emitting display device which can prevent short circuit betweentwo electrodes driving an organic light-emitting element in alight-emitting element due to the surface roughness of the substrate andprovide an improved aperture ratio.

2. Description of the Related Art

As real multi-media era is coming up, flat panel displays (hereinafter,abbreviated to FPDs) used as a man-machine interface are being widelynoticed. Conventionally, liquid crystal displays (hereinafter,abbreviated to LCDs) have been used as the FPDs. However, the LCDs havedrawbacks such as their slow response and a narrow viewing anglecompared with CRT displays.

Recently, as one of the next generation FPDs, display devices usingorganic light-emitting devices have attracted a great deal of attention.The device using the organic light-emitting device (hereinafterabbreviated to OLED) has superior properties such as spontaneous lightemission, wider viewing angle, faster response speed and the like.Conventional structure of OLED is based on a stack of a first electrodepreferably formed on glass, an organic light-emitting layer comprising ahole transport layer, a light-emitting layer and an electron transportlayer formed on the first electrode, and a second electrode as an upperelectrode with a low work function formed on the organic light-emittinglayer. Then, by applying a voltage of several volts between the firstand the second electrodes, holes and electrons are injected into thehole transport layer and the electron transport layer, respectively.Next, excitons are formed in the light-emitting layer where the holesand the electrons are combined. Finally, light is emitted from thelight-emitting layer when the excitons formed return to their groundstates. In the case of a so-called bottom emission type using the firstelectrode which is transparent, the emitted light passes the firstelectrode and is taken out from the back of the substrate.

Display devices using OLEDs are classified into two groups. One is theOLED of a simple matrix type and another is the OLED of an active matrixtype. In the case of the simple matrix type, organic layers, comprisinghole transport layers, light-emitting layers and electron transportlayers, are formed on the positions where a plurality of anode lines (oranode wirings) and cathode lines (or cathode wirings) cross each other.Each pixel is lit up only for a preset period during one frame. Thepreset period is the time interval of the one frame divided by thenumber of the anode lines. The OLED of the simple matrix type has anadvantage of its simpler structure.

However, in the case of the simple matrix type, if the number of pixelsincreases, the preset period should become shorter. Therefore, toachieve a required value for averaged luminance, it is necessary toincrease the luminance of the pixel during the preset period. In thiscase, it causes a problem of a shortened life of the OLED. Furthermore,particularly for a large display panel of OLED, as the OLED is driven byDC, non-uniform potential is applied to each pixel because of thepotential drop due to elongated lengths of the anode and cathode lines.As a result, non-uniform luminance is generated over the entire displayarea. Therefore, qualities in terms of high definition of the picturesand scaling-up of the display size are limited for the simple matrixtype.

On the other hand, in the case of an OLED of an active matrix type, eachorganic light-emitting element comprising each pixel is connected to anelement driving circuit (or a pixel driver) comprising 2 to 4 switchingelements such as thin film transistor (hereinafter abbreviated to TFT)and capacitors. Also, power lines are formed to supply current to eachlight-emitting element and thereby all pixels can be simultaneouslyoperated during the period of one frame. Thus, it is not necessary toincrease the luminance of the pixels all together and their lives can beelongated. From these reasons, to achieve high definition of picturesand scaling-up (or large display size), the OLED of the active matrixtype has an advantage over other types of the OLEDs. Hereinafter, TFTsare used for the switching elements but other active elements can beused instead.

The OLED of the active matrix type which emits light from the back ofthe substrate is called “bottom emission type”. In the OLED of thistype, as the pixel driving elements are installed between the substrateand organic light-emitting elements, as the pixel driving elementsobstruct the light emitted from the light-emitting elements and apertureratio is restricted. Particularly, in the case of large area displays,widths of power lines are widened to reduce the non-uniformity of theluminance of pixels due to potential drop along the power lines, whichbrings a problem that the aperture ratio of the display becomes smaller.Additionally, if the capacitances of the capacitors are increased topreserve the bias and signal voltages of the transistors to drive theOLED, the area of the capacitor electrodes increases, which accordinglycauses a problem that the aperture ratio becomes extremely small.

To solve above problems, efforts to emit the light from the upperelectrode using transparent electrode are being made. The OLED with thestructure of light emission from the upper electrode is called “a topemission type”. However, in the structure of the top emission type,light-emitting units of OLED are formed on the TFTs, capacitorelectrodes or wirings, which causes a problem of a short circuit betweenthe bottom and the upper electrode. It is because the organiclight-emitting layer which forms a light-emitting unit and is very thin(about 50-200 nm) can not cover the surface roughness of its underlyinglayer. This is one of the problems to be sorted out.

To solve this problem, an OLED using a polyimide film as a flatteninglayer to reduce the surface roughness of its underlying layer wasdisclosed in JP-A No. 10-189252, which is incorporated herein byreference. FIG. 11 illustrates a sectional view of a structure of apixel region in the conventional OLED showing the flattening layerformed on its underlying layer. Referring to FIG. 11, a gate insulatingfilm 117 covering a lower capacitor electrode 105 and an upper capacitorelectrode 108 are formed on a glass substrate 116. A capacitor whichconsists of a stack of the lower capacitor electrode 105, the gateinsulating film 117 and the upper capacitor electrode 108 is formed.

A 1st insulating interlayer 118 is formed on the stack of the capacitor.On the capacitor, a power line 110 is formed and connected to the uppercapacitor electrode 108. Here, a signal line 109 is formedsimultaneously. A 2nd insulating interlayer 119 is formed covering thepower line 110 and the signal line 109. The flattening layer 136 isformed on the 2nd insulating interlayer 119 and provides a flat surfacefor a deposition of a lower electrode 115 to form an organiclight-emitting element. Reference numeral 120 denotes a 3rd insulatinginterlayer 120 which prescribes a region of a light-emitting unit 135.Reference numeral 126 denotes a protective layer.

FIG. 12 shows a schematic equivalent circuit diagram of a drivingcircuit for the organic light-emitting element in the OLED shown in FIG.11. The same reference numerals shown in FIG. 11 are correspondinglynumbered in FIG. 12. Referring to FIG. 12, one pixel consists of anorganic light-emitting element 100, a 1st TFT 101 connected to ascanning line 106 and a signal line 109, a 2nd TFT 102 connected to apower line 110 and a capacitor 104. The scanning line 106 selects theTFT 101 and a signal (i.e. data to be displayed) from the signal line109 is stored in the capacitor 104. Based on the signal stored in thecapacitor 104, the 2nd TFT 102 provides a current from the power line110 for the organic light-emitting element 100 and then the organiclight-emitting element 100 emits light.

Therefore, in the conventional OLED, the surface roughness of the lowercapacitor electrode 105 and the upper electrode for the capacitor 108and steps formed by the power line 110 and the signal line 109 can notbe eliminated by the 2nd insulating interlayer 119. Accordingly, a thickflattening layer 136 must be formed to flatten the light-emitting unit135 consisting of the lower electrode 115, an electron injection layer124, an electron transport layer 123, a light-emitting layer 122, a holetransport layer 121 and the upper electrode 125. However, to introducethe above flattening layer 136, it requires additional processes such asa spin coating, a baking process, a patterning process using aphotolithography, etc, which degrades the reliability of the totalprocess.

In short, based on the prior art, the structure of the OLED of the topemission type is required to ensure a high aperture ratio. Accordingly,the flattening layer 136 with thickness of several μm is necessary toavoid a short circuit between the lower electrode 115 and the upperelectrode 125 herewith, where the short circuit is caused by the surfaceroughness originated from the underlying layers comprising the TFT,wirings, etc.

Thus, a purpose of the present invention is to provide an OLED of thetop emission type comprising organic light emitting elements bypreventing the previous problems such as the widening of the powerlines, the reduction in the aperture ratio caused by the widening of theupper and the lower capacitor electrodes and the short circuit betweenthe upper and the lower electrodes caused by the roughness of theflattening layers.

SUMMARY OF THE INVENTION

The present invention provides an organic light-emitting display devicecomprising a plurality of pixels having organic light-emitting elementswhich comprise organic light-emitting layers sandwiched between upperand lower electrodes, wherein light emitted from the organic layer istaken out from the side of the upper electrode and, in each pixel, aregion of light-emitting layer substantially sandwiched between theupper and lower electrodes is formed on a power line of TFT for drivingthe pixel.

The present invention provides another organic light-emitting displaydevice comprising a plurality of pixels having organic light-emittingelements which comprise organic light-emitting layers sandwiched betweenupper and lower electrodes, wherein light emitted from the organic layeris taken out from the side of the upper electrode and, in each pixel,the region of light-emitting layer substantially sandwiched between theupper and lower electrodes is formed on the electrode forming acapacitor connected to the TFT for driving the pixel.

In an organic light-emitting device of the present invention, basically,a pixel driving unit for actively driving pixels comprises a circuit of2-4 pieces of TFTs and capacitors. However, the number of the TFTs isnot restricted to the number 2-4 but it may be more than 4. Also,structures of the TFTs used in a circuit of a pixel driving unit foractively driving can be a coplanar type, an inverted-stagger type or anormal stagger type. Here, the capacitors have two kinds of functions.One is to hold a bias voltage of the TFTs for actively driving. Anotheris to hold a signal voltage. The electrodes to functionalize thecapacitors can be lower capacitor electrodes or upper capacitorelectrodes. Preferably, the electrodes to functionalize the capacitorsare the upper capacitor electrodes to enlarge the aperture ratioeffectively. Two kinds of TFTs are incorporated consisting of the TFTsto control the signals for the display and the TFTs to drive the pixelsbased on the signals.

To fabricate an organic light-emitting display device of the presentinvention, preferably, an upper electrode is at least one of thecomponents selected from a group of transparent conductive oxides,transparent metal thin films and organic conductive films. In thepresent specification, the description “pixel” means minimum unit, aplurality of which are arranged on a screen of an organic light-emittingdevice to display characters or graphics. In the case of a full-colordisplay, each pixel consists of sub-pixels of three colors, namely,green, red and blue.

There are two different structures suitable for the fabrication of theorganic light-emitting devices. One is the structure where a lowerelectrode is an anode and an upper electrode is a cathode. In thisstructure, a first injection layer and a first transport layer serve asa hole injection layer and a hole transport layer, respectively. Then, asecond injection layer and a second transport layer serve as an electroninjection layer and an electron transport layer, respectively. Anotherstructure comprises the lower electrode as a cathode and the upperelectrode as an anode. In this structure, a first injection layer and afirst transport layer serve as an electron injection layer and anelectron transport layer, respectively. Then, a second hole layer and asecond transport layer serve as a hole injection layer and a holetransport layer, respectively. In these two kinds of structures, it ispossible to delete the first injection layer or the second injectionlayer. Additionally, the first transport layer or the second transportlayer may serve as the light-emitting layer.

An anode is preferably composed of a conductive film with a large workfunction to enhance an injection rate of the holes. The anode can beformed of, for example, Au, Pt, etc but it is not restricted to them.Materials selected from the group of transparent conductive oxides suchas In₂O₃—SnO₂ and In₂O₃—ZnO can be also used for the anode. Thesetransparent conductive oxide films can be deposited using conventionalsputtering, EB-evaporation, ion-plating and the like.

Work functions of In₂O₃—SnO₂ and In₂O₃—ZnO films are both about 4.6 eVwhich can be increased to 5.2 eV by a UV irradiation or a plasmatreatment using oxygen. In the case of In₂O₃—SnO₂ films, these filmsbecome poly-crystalline when they are deposited at a substratetemperature about 200° C. However, as the poly-crystalline states yielddifferent etching rates in grains and grain boundaries of those films,amorphous states are preferred when they are to be used for the lowerelectrodes.

When an anode is used with the hole injection layer, the materials withlager work functions are not required to form the anode and it ispossible to use ordinary conductive films such as metals including Al,In, Mo, Ni and Cr, their alloys and inorganic materials such as poly-Si,amorphous-Si, tin oxides, indium oxides and indium-tin oxides (ITO).Also, organic materials and conductive inks comprising polyaniline,polythiophene, etc, can be used and formed by a conventional coatingprocess suitably selected. Materials for the anode are not restricted tothose described above and simultaneous use of two or more materials maybe effective.

As a hole injection layer, materials having suitable ionizationpotentials are preferably selected to reduce the injection barrierbetween the anode and the hole transport layers. The hole transportlayer is formed preferably to fill up the roughness of the underlyinglayer. The hole injection layer can be selected from the groupconsisting of, for example, Cu-phthalocyanines, star-burst aminecompounds, polyanilines, polythiophenes, vanadium oxides, molybdenumoxides, ruthenium oxides, aluminum oxides, etc but it is not restrictedto them.

A hole transport layer is formed to transport and inject holes into thelight-emitting layer. For that purpose, the hole transport layer ispreferably selected from the group of materials which have higher holemobility and are chemically stable. Additionally, the hole transportlayer is preferably selected from the group of materials which havelower electron affinity and higher glass transition temperature. Forthese purposes, the hole transport layer is preferably formed of, forexample,N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′diamine(TPD), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD),4,4′,4″-tri (N-carbazolyl)triphenylamine (TCTA), 1,3,5-tris[N-(4-diphenylaminophenyl)phenylamino]benzene (p-DPA-TDAB) but it is notrestricted to them and simultaneous use of two or more materials ispossible.

A light-emitting layer is a layer where injected holes and electronsrecombine and emit light at wavelengths intrinsic to the materials used.There are two cases for the light emission. One is the case that thehost material comprising the light-emitting layer emits light. Anotheris that a small quantity of dopant material itself doped in the hostmaterial emits light. As heterothallic host materials, the followingmaterials can be used preferably: distylylarylene derivatives (DPVBi),silole derivatives with benzene skelton (2PSP), oxodiazole derivativeswith triphenylamine on both ends (EM2), perynone derivative withphenanthrene group (P1), oligothiophene derivatives with triphenylaminestructures on both ends (BMA-3T), perylene derivatives (tBu-PTC), tris(quinolinol) aluminum, poly-paraphenylene-vinylene derivatives,polythiophene derivatives, poly-paraphenylene derivatives, polisilanederivatives, polyacetylene derivarives. Materials which can be used forthis purpose are not restricted to those listed above and two or more ofthem can be simultaneously used.

Next, as a dopant material, the following can be used preferably:quinacridone, coumarin 6, Nile red, rubrene,4-(dicyanomethylene)-2-methyl-6-(para-dimethylaminostyryl)-4H-pyran(DCM), dicarbazole derivatives. Materials which can be used for thispurpose are not restricted to those and two or more of them can besimultaneously used.

An electron transport layer transports electrons and inject them intothe light-emitting layer. For this purpose, desirably it a has highelectron mobility. For example, tris (8-quinolinol) aluminum, oxadiazolederivatives, silole derivatives, zinc-benzothiazole complexes are usedfavorably. It is not restricted to these materials and two or more ofthem may be used simultaneously.

An electron injection layer is used to enhance the efficiency ofelectron injection from the cathode to the electron transport layer. Thefollowing materials can be used preferably: lithium fluoride, magnesiumfluoride, calcium fluoride, strontium fluoride, barium fluoride,magnesium oxide. Materials which can be used for this purpose are notrestricted to those and two or more of them can be simultaneously used.

A conductive film with a low work function to enhance efficiency ofelectron injection is favorable for the cathode. Preferably, thefollowing materials can be used: magnesium, silver alloys, aluminum,lithium alloys, aluminum-calcium alloys, aluminum-magnesium alloys,metallic calcium, cerium compounds, but it is not restricted to them.

If the electron injection layer is formed, it is not necessary to use amaterial with a low work function for the cathode. Instead, commonlyused metal may be used for this purpose. Preferably, the followingmaterials can be used: metals such as aluminum, indium, molybdenum,nickel, chromium, their alloys, poly-silicon, amorphous-silicon, etc.

When a cathode is used for an upper electrode, it is preferable to forman electron injection layer under the cathode. By forming an electroninjection layer, it is possible to use transparent conductive films withlarge work functions. For example, transparent conductive films based onIn₂O₃—SnO₂ or In₂O₃—ZnO can be used. These transparent electrodematerials can be fabricated using a sputtering, EB-evaporation,ion-plating method and the like.

A protective layer is formed on the upper electrode to prevent H₂O andO₂ in the atmosphere from penetrating into the upper electrode or theunderlying organic layers. For example the following materials arepreferably used: inorganic materials such as SiO₂, SiN_(x),SiO_(x)N_(y), Al₂O₃, etc and organic materials such as polychloroprene,polyethylene terephthalate, polyoxymethylene, polyvinyl chloride,polyvinylidene fluoride, cyanoethyl pullulan, polymethyl methacrylate,polysulfone, polycarbonate, polyimide, etc. It is not restricted tothose materials.

While the present invention has been particularly shown and describedwith reference to preferred methods and materials thereof, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope of the present invention as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a plan view of a configuration of an OLED according to theembodiment 1 of the present invention.

FIG. 2 is a sectional view of the light-emitting element taken alongline A-A′ of FIG. 1.

FIG. 3 shows a cross cut section of the region including alight-emitting element in OLED taken along line A-A′ of FIG. 1,illustrating a modification of the OLED according to the embodiment 1 ofthe present invention.

FIG. 4 shows a cross cut section of the region including light-emittingelement in OLED taken along line A-A′ of FIG. 1, illustrating anothermodification of the OLED according to the embodiment 1 of the presentinvention.

FIG. 5 shows a cross cut section of the region including alight-emitting element in OLED taken along line A-A′ of FIG. 1,according to the embodiment 2 of the present invention.

FIG. 6 is a plan view of the substantial part in an OLED according tothe embodiment 3 of the present invention.

FIG. 7 is a plan view of the substantial part in an OLED according tothe embodiment 4 of the present invention.

FIG. 8 shows a cross cut section of the region including alight-emitting element in the OLED taken along line A-A′ of FIG. 1,according to the embodiment 4 of the present invention.

FIG. 9 is a plan view of the substantial part in an OLED according tothe embodiment 5 of the present invention.

FIG. 10 shows a cross cut section of the region including alight-emitting element in the OLED taken along line A-A′ of FIG. 1,according to the embodiment 4 of the present invention.

FIG. 11 is a sectional view of a structure of a pixel region in theconventional OLED showing the flattening layer formed on its underlyinglayer.

FIG. 12 is a schematic equivalent circuit diagram of a driving circuitfor the organic light-emitting element in the OLED shown in FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of organic light-emitting display device according to thepresent invention will be described with reference to the appendeddrawings.

Embodiment 1

FIG. 1 is a plan view of a configuration of an OLED according to theembodiment 1 of the present invention. FIG. 2 is a sectional view of thelight-emitting element taken along line A-A′ of FIG. 1. The OLED shownin FIGS. 1 and 2 comprises plural light-emitting elements, each of whichis arranged in a matrix and has an organic light-emitting element. Theorganic light-emitting element consists of an organic light-emittinglayer 122 and an upper electrode 125 and a lower electrode 115sandwiching the organic light-emitting layer 122. This organiclight-emitting element is the type of the top emission where light isemitted from the organic light-emitting layer 122 and then the light istaken out from the upper electrode 125. Reference numerals 121, 123, 124and 126 denote a hole transport layer, an electron transport layer, anelectron injection layer and an protective layer, respectively.

In FIG. 1, reference numeral 101 denotes a 1st TFT. Reference numerals112, 113, 103 and 107 relate to the 1st TFT and denote a sourceelectrode, a drain electrode, an active layer consisting of a-Si and agate electrode thereof, respectively. Reference numeral 102 denotes a2nd TFT. Reference numerals 112′, 113′, 103′ and 107′ relate to the 2ndTFT and denote a source electrode, a drain electrode, an active layerconsisting of a-Si and a gate electrode thereof, respectively. The 1stTFT 101 is a TFT (TFT for control) which controls the 2nd TFT (TFT fordriving) driving the organic light-emitting element.

Reference numerals 104, 105, 108, 106, 109 and 110 denote a capacitor, alower capacitor electrode, an upper capacitor electrode, a scan line, asignal line and a power line, respectively. Typical feature of theconfigurations of this embodiment is that a light-emitting unit 135,substantially an organic light-emitting element, is formed on the powerline 110.

Hereinafter, a manufacturing method of the OLED according to theembodiment 1 of the present invention will be explained. First,amorphous silicon (hereinafter, abbreviated to a-Si) with film thickness50 nm is formed on a glass substrate 116 using LPCVD (Low Pressure CVD).Then the total area of the a-Si is laser-annealed and then the a-Si iscrystallized to form poly-crystalline Si (hereinafter, abbreviated top-Si). Next, by patterning the p-Si using dry etching, an active layer103 for the 1st transistor 101, an active layer 103′ for the 2ndtransistor 102 and a lower capacitor electrode 105 are formed. Afterthat, a gate insulating film 117 of SiO₂ with thickness 100 nm is formedby plasma enhanced chemical vapor deposition (hereinafter, abbreviatedto PECVD).

Next, two gate electrodes 107 and 107′ of TiW with thickness 50 nm forthe two TFT's are formed using a sputtering and then patterned withprescribed patterns. Simultaneously to these processes, the scan line106 and the upper capacitor electrode 108 are patterned, which isfollowed by forming a gate insulating film 117 over them. Next, P ionsare injected into the patterned p-Si from the top of the gate insulatingfilm 117 using an ion implantation. Here, the P ions are not injected tothe region where the gate electrodes 107 and 107′ are formed. Thereby,the active layer 103 and 103′ are completed.

Next, the glass substrate 116 is activated in an inert atmosphere (N₂)by heating so that the doping can be effectively carried out. On theglass substrate 116, a 1st insulating interlayer 118 of silicon nitride(SiNx) with thickness 200 nm is formed.

Next, a contact hole is formed in the gate insulating film 117 and the1st insulating interlayer 118 on upper both ends of the active layers103 and 103′. Furthermore, another contact hole is formed in the 1stinsulating interlayer 118 on the upper side of the gate electrode 107′for the 2nd TFT. Here, the contact hole is described as disrupted stateof the 1st insulating interlayer 118 as shown in FIG. 2. On the contacthole, Al film with thickness 500 nm is formed by a sputtering and thenby a photolithographic process the signal line 109 and the power line110 are formed. Then, the source electrode 112 and the drain electrode113 for the 1st TFT, and the source electrode 112′ and the drainelectrode 113′ for the 2nd TFT are formed.

Then, the lower capacitor electrode 105 and the drain electrode 113 ofthe 1st TFT 101 are connected. The source electrode 112 of 1st TFT 101and the signal line 109, the drain electrode 113 of 1st TFT and the gateelectrode 107′ of 2nd TFT 102, and, the drain electrode 113′ of 2nd TFTand the power line 110 are connected. Finally, the upper capacitorelectrode 108 is connected to the power line 110.

Next, a 2nd insulating interlayer 119 of SiNx with thickness 500 nm isformed to cover the power line 110. The contact hole is formed on top ofthe source electrode 112′ for the 2nd TFT. On the contact hole, using asputtering, Al film with thickness 150 nm is formed and then the lowerelectrode 115 is formed by photolithography. Then, by a spin coattechnique using, for example, a positive type of protective film oflight sensitive resin (PC452, JSR Corporation), a 3rd insulatinginterlayer 120 is formed and baked. Preferably, the thickness of the 3rdinsulating interlayer 120 consisting of the positive type lightsensitive resin protective film (PC452) is 1 μm and is formed to coverthe edge of the lower electrode 115 by about 3 μm.

FIG. 2 illustrates the cross section of the structure of thelight-emitting element comprising of the organic the light-emittingelement.

The glass substrate 116 with a stack up to the lower electrode 115 isultrasonically cleaned with an acetone and pure water in this order eachfor three minutes. After the cleaning, the glass substrate 116 isspin-dried. Next, an electron injection layer 124 of LiF with thickness0.5 nm is formed on the lower electrode 115 by a vacuum depositionmethod. During the formation of the electron injection layer 124, ashadow mask is used to form its pattern.

On the electron injection layer 124, a film of Alq (tris (8-quinolinol)aluminium) with thickness 20 nm is formed using a vacuum depositionmethod. This film of the Alq serves as an electron transport layer 123.During the formation of the electron transport layer 123, a shadow maskis used to form its pattern. On the electron transport layer 123,co-deposition of Alq (tris (8-quinolinol) aluminium) and quinacridone(Qc) with thickness 20 nm is performed by simultaneous vacuum depositionmethod with two sources. The co-deposited film of Alq and Qc serves as alight-emitting layer 122 and its pattern is formed using a shadow mask.

Next, a film of 4,4-bis[N-(1-naphtyl)-N-phenylamino]biphenyl(hereinafter, abbreviated to α-NPD) with thickness 50 nm is formed by avacuum deposition method using a shadow mask for its patterning. Regionof the deposition is 1.2 times each edge of the lower electrode 115.This film of the α-NPD serves as a hole transport layer 121.

Next, by a sputtering method, a film of In-Zn-O (hereinafter,abbreviated to IZO film) with thickness 50 nm is formed. This IZO filmserves as an upper electrode 125 and is amorphous. As a target for thesputtering, a composition of In/(In+Zn)=0.83 is used for the targetfabrication. Sputtering conditions of a vacuum pressure at 1 Pa with amixed gas of Ar:O₂ and a sputtering power of 0.2 W/cm² are used. Theupper electrode 125 consisting of In-Zn-O serves as an anode withtransmittance over 80%. Next, by a sputtering method, a film ofSi_(x)N_(y) with thickness 50 nm is formed and serves as a protectivelayer 126.

As shown in FIG. 2, the OLED according to the embodiment 1 of thepresent invention comprises the light-emitting unit 135 consisting ofthe lower electrode 115 only formed on the flat portion of the powerline 110, the organic light-emitting layer 122 and the upper electrode125. Therefore, by fabricating this structure, without forming aflattening layer on the light-emitting layer, there is no electric shortcircuit between the lower electrode 115 and upper electrode 125 usuallycaused by the surface roughness of the stack.

FIG. 3 shows a cross cut section of the region including alight-emitting element in OLED taken along line A-A′ of FIG. 1,illustrating a modification of the OLED according to the embodiment 1 ofthe present invention. In the structure of this OLED, an upper electrode108 and a power line 110 are commonly used. Using this structure,capacitance can be enhanced. Other advantageous effects are the same asthose of the embodiment 1 explained for the FIGS. 1 and 2.

FIG. 4 shows a cross cut section of the region including light-emittingelement in OLED taken along line A-A′ of FIG. 1, illustrating anothermodification of the OLED according to the embodiment 1 of the presentinvention. In the structure of this OLED, a lower capacitor electrode105 and an upper capacitor electrode 108 are widened under a power line110. Using this structure, capacitance can be enhanced more than thatshown in FIG. 3. Other advantageous effects are the same as those of theembodiment 1 explained for the FIGS. 1 and 2.

Embodiment 2

Now, an OLED using an upper electrode as a cathode will be explainedbelow. FIG. 5 shows a cross cut section of the region including alight-emitting element in OLED taken along line A-A′ of FIG. 1,according to the embodiment 2 of the present invention. The OLED of theembodiment 2 comprises an upper electrode 125 as a cathode and a lowerelectrode 115 as an anode, which is different from the structure of theprevious embodiment 1. Hereinafter, the manufacturing method in theembodiment 2 will be explained.

First, amorphous silicon (a-Si) with film thickness 50 nm is formed on aglass substrate 116 using LPCVD (Low Pressure CVD). Then the total areaof the a-Si is laser-annealed and the a-Si is crystallized to formapoly-crystalline Si (p-Si). Next, by patterning the p-Si using a dryetching, an active layer 103 for a 1st transistor 101, an active layer103′ for a 2nd transistor 102 and a lower capacitor electrode 105 areformed.

After that, a gate insulating film 117 of SiO₂ with thickness 100 nm isformed. The SiO₂ film is formed by a PECVD using tetraethoxysilane(TEOS) as a source. Next, gate electrodes 107 and 107′ of TiW withthickness 50 nm for the corresponding TFT's are formed using asputtering and then patterned with prescribed patterns. Simultaneouslyto this process, a scan line 106 and an upper capacitor electrode 108are patterned.

Next, ions of P and B are injected into the gate insulating films 117and 117′ to make the 1st TFT n-type and the 2nd TFT p-type,respectively. After that, the glass substrate 116 is activated in aninert atmosphere (N₂) by heating so that the doping can be effectivelycarried out. On the glass substrate 116, a 1st insulating interlayer 118of silicon nitride (SiN_(x)) with thickness 200 nm is formed.

Next, contact holes are formed in the gate insulating film 117 and 1stinsulating interlayer 118 on upper both ends of the active layers 103and 103′. Furthermore, an additional contact hole is formed in the 1stinsulating interlayer 118 on the upper side of the gate electrode 107′for the 2nd TFT. Here, the contact hole is described as disrupted stateof the 1st insulating interlayer 118 as shown in FIG. 5. On the contacthole, Al film with 500 nm is formed by a sputtering and then byphotolithographic process a signal line 109 and a power line 110 areformed. Then, a source electrode 112 and a drain electrode 113 for the1st TFT, and a source electrode 112′ and a drain electrode 113′ for the2nd TFT are formed.

Then, the lower capacitor electrode 105 and the drain electrode 113 ofthe 1st TFT 101 are connected. The source electrode 112 of the 1st TFT101 and the signal line 109, the drain electrode 113 of the 1st TFT andthe gate electrode 107′ of the 2nd TFT 102, and, the drain electrode113′ of the 2nd TFT and the power line 110 are connected. Finally, theupper capacitor electrode 108 is connected to the power line 110.

The 2nd insulating interlayer 119 of SiNx with thickness 500 nm isformed to cover the power line 110. A contact hole is formed on top ofthe source electrode 112′ for the 2nd TFT. On the contact hole, usingsputtering, ITO film with thickness 150 nm is formed and then a lowerelectrode 115 is formed by photolithography.

Next, by a spin coat using, for example, a positive type of protectivefilm of light sensitive resin (PC452, JSR Corporation), a 3rd insulatinginterlayer 120 is formed and baked. Preferably, the thickness of the 3rdinsulating interlayer 120 consisting of the positive type lightsensitive resin protective film (PC452) is 1 μm and is formed to coverthe edge of the lower electrode 115 by about 3 μm.

Next, a fabrication method of the light-emitting element comprising ofthe organic the light-emitting element will be explained.

The glass substrate 116 with a stack up to the lower electrode 115 isultrasonically cleaned with an acetone and pure water in this order eachfor three minutes. After cleaning, the glass substrate 116 is spin-driedand oven-dried at 120° C. for 30 minutes. On the lower electrode 115, afilm of 4,4-bis[N-(1-naphtyl)-N-phenylamino]biphenyl (α-NPD) withthickness 50 nm is formed by a vacuum deposition method using a shadowmask for its pattern. Region of the deposition is 1.2 times each edge ofthe lower electrode 115. This film of the α-NPD serves as a holetransport layer 121.

On the hole transport layer 121, co-deposition of Alq (tris(8-quinolinol) aluminium) and quinacridone (Qc) with thickness 20 nm isperformed by a simultaneous vacuum deposition method with two sources.The co-deposition is carried out by controlling each deposition rate ata ratio of Alq to Qc=40:1. Its pattern is formed using a shadow mask.The co-deposited film of Alq+Qc serves as a light-emitting layer 122.Then Alq with thickness 20 nm is deposited on the light-emitting layer122 using a vacuum deposition method using a shadow mask to form itspattern. This film of Alq serves as an electron transport layer 123.

On the electron transport layer 123, an alloy film of Mg and Ag isformed as an electron injection layer 124. This film is deposited usinga simultaneous vacuum deposition method with two sources. A depositionrate of Mg to Ag is controlled at 14:1 and the thickness is 10 nm. Ashadow mask is used for its patterning.

Next by a sputtering method, a film of In-Zn-O (hereinafter, abbreviatedto IZO film) with thickness 50 nm is formed. This IZO film serves as anupper electrode 125 and is amorphous. As a target for the sputtering, acomposition of In/(In+Zn)=0.83 is used for the fabrication of thetarget. Sputtering conditions of a vacuum pressure at 1 Pa with mixedgas of Ar:O₂ and a sputtering power of 0.2 W/cm² are used. The upperelectrode 125 consisting of Mg:Ag/In-Zn-O serves as a cathode withtransmittance 70%. Next, by a sputtering method, a film of Si_(x)N_(y)with thickness 50 nm is formed and serves as a protective layer 126.

The OLED according to the embodiment 2 has the lower electrode 115 whichis transparent. The emitted light passing toward the glass substrate 116is reflected by the power line 110 and is taken out from the protectivelayer 126, which improves the efficiency of the light emission.

The OLED according to the embodiment 2 of the present inventioncomprises the light-emitting unit 135 consisting of the lower electrode115 formed only on the flat portion of the power line 110, the organiclight-emitting layer 122 and the upper electrode 125. Therefore, byfabricating this structure, without forming a flattening layer on thelight-emitting layer, there is no electric short circuit between thelower electrode 115 and the upper electrode 125, while the short circuitis usually caused by the surface roughness of the stack.

Embodiment 3

FIG. 6 is a plan view of the substantial part in an OLED according tothe embodiment 3 of the present invention. TFTs of inverted-staggerstructure are applied to this embodiment 3, where a 1st TFT 101 and a2nd TFT are formed by the inverted-stagger structures, dissimilar to theprevious embodiments 1 and 2. The reference numerals in the FIG. 6denote the same meanings as those shown in FIG. 1. Hereinafter, amanufacturing method of the OLED according to the embodiment 3 will beexplained.

First, a gate electrode 107 of the 1st TFT 101 and a gate electrode 107′of the 2nd TFT 102 are formed using TiW with thickness 50 nm by asputtering and then patterned with prescribed patterns. Simultaneouslyto this process, a scan line 106 and a lower capacitor electrode 105 arepatterned. Next, a gate insulating film 117 of SiO₂ with thickness 100nm is formed. The SiO₂ film is formed by a plasma enhanced CVD (PECVD)using tetraethoxysilane as a source.

Next, a film of amorphous silicon (a-Si) with thickness 50 nm is formedusing a LPCVD (Low Pressure CVD). Then the total area of the the a-Sifilm is laser-annealed and the a-Si film is crystallized to form apoly-crystalline Si (p-Si). Next, by patterning the p-Si using dryetching, an active layer 103 for the 1st transistor 101, an active layer103′ for the 2nd transistor 102 and an upper capacitor electrode 108 areformed. After that, a stopper film consisting of SiO₂ (not shown in theFIG. 6) is formed on the p-Si. This SiO₂ film is formed by a plasmaenhanced CVD (PECVD) using tetraethoxysilane as a source and thenpatterned.

Next, ions of P are injected into the p-Si layer patterned by anion-implantation method. The ions of P are not injected to the regionson which the stopper film is present. Then, active layers 103 and 103′are formed. After that, the glass substrate 116 is activated in an inertatmosphere (N₂) by heating so that the doping can be effectively carriedout. On the glass substrate 116, a 1st insulating interlayer 118 ofsilicon nitride (SiNx) with thickness 200 nm is formed.

Next, contact holes are formed in the 1st insulating interlayer 118 onupper both ends of the active layers 103 and 103′.

Furthermore, another contact hole is formed in the gate insulating film117 and the 1st insulating interlayer 118 on the upper side of the gateelectrode 107′ for the 2nd TFT. On the contact hole, Al film withthickness 500 nm is formed by a sputtering. Then, by a photolithographicprocess, a signal line 109 and a power line 110 are formed. Then, asource electrode 112 and a drain electrode 113 of the 1st TFT, and asource electrode 112′ and a drain electrode 113′ of the 2nd TFT areformed.

Then, the lower capacitor electrode 105 and the drain electrode 113 ofthe 1st TFT 101 are connected. The source electrode 112 of the 1st TFT101 and the signal line 109, the drain electrode 113 of the 1st TFT andthe gate electrode 107′ of the 2nd TFT 102, and, the drain electrode113′ of the 2nd TFT and the power line 110 are connected. Finally, theupper capacitor electrode 108 is connected to the power line 110.

A 2nd insulating interlayer 119 of SiNx with thickness 500 nm is formedto cover the power line 110. A contact hole is formed on top of thesource electrode 112′ of the 2nd TFT. On the contact hole, using asputtering, Al film with thickness 150 nm is formed and then a lowerelectrode 115 is formed by a photolithography.

As a 3rd insulating interlayer 120, by a spin coat using a positive typeof protective film of light sensitive resin (for example, PC452, JSRCorporation), the 3rd insulating interlayer 120 is formed and baked.Preferably, the thickness of the 3rd insulating interlayer 120,consisting of the positive type of protective film of light sensitiveresin (PC452), is 1 μm and is formed to cover the edge of the lowerelectrode 115 by about 3 μm.

The structure of the organic light-emitting element and the fabricationmethod of the protective layer are the same as those described in theprevious embodiment 1.

The OLED according to the embodiment 3 of the present inventioncomprises the light-emitting unit 135 consisting of the lower electrode115 formed only on the flat portion of the power line 110, the organiclight-emitting layer 122 and the upper electrode 125. Therefore, byfabricating this structure, without forming a flattening layer on thelight-emitting layer, there is no electric short circuit between thelower electrode 115 and upper electrode 125, while the short circuit isusually caused by the surface roughness of the stack.

Embodiment 4

FIG. 7 is a plan view of the substantial part in an OLED according tothe embodiment 4 of the present invention. FIG. 8 shows a cross cutsection along line A-A′ of the region including a light-emitting elementin OLED corresponding to FIG. 1, according to the embodiment 4 of thepresent invention. The OLED of this embodiment 4 comprises an organiclight-emitting element formed on a capacitor which forms a capacitanceto hold a bias voltage for the TFT.

The OLED of this embodiment 4 comprises a plurality of light-emittingelements, each of which consists of an organic light-emitting layer 122,an upper electrode 125 and a lower electrode 115 sandwiching an organiclight-emitting layer 122. This organic light-emitting element is thetype of top emission where light is emitted from the organiclight-emitting layer 122 and then the light is taken out from the upperelectrode 125. A substantial light-emitting unit 135 of the organiclight-emitting element is formed on an upper capacitor electrode 108.Hereinafter, a manufacturing method of this embodiment 4 is the same asthat described in the previous embodiment 1.

As shown in FIG. 8, the OLED according to the embodiment 3 of thepresent invention comprises the light-emitting unit 135 consisting ofthe lower electrode 115, light-emitting layer and the upper electrode125 only formed on the flat portion of the upper capacitor electrode 108forming a capacitance to hold a bias voltage for the TFT to drive thelight-emitting element. Therefore, by fabricating this structure,without forming a flattening layer on the light-emitting layer, there isno electric short circuit between the lower electrode 115 and upperelectrode 125 while the short circuit is usually caused by the surfaceroughness of the stack.

Embodiment 5

FIG. 9 is a plan view of the substantial part in an OLED according tothe embodiment 5 of the present invention. FIG. 10 shows a cross cutsection of the region including a light-emitting element in the OLEDtaken along line A-A′ of FIG. 1, according to the embodiment 4 of thepresent invention.

The OLED of this embodiment 5, differing to the embodiment 1, comprisesan organic light-emitting element formed on the capacitor which forms acapacitance to hold the signal voltage for a TFT controlling a TFT todrive the organic light-emitting element.

Hereinafter, a manufacturing method of this embodiment 5 will beexplained.

First, a film of amorphous silicon (a-Si) with thickness 50 nm is formedon a glass substrate 116 using LPCVD (Low Pressure CVD). Then the totalarea of the a-Si is laser-annealed and the a-Si is crystallized to forma poly-crystalline Si (p-Si). Next, by patterning the p-Si using dryetching, an active layer 103 for a 1st transistor 101, an active layer103′ for a 2nd transistor 102 and a lower capacitor electrode 105 areformed.

After that, a gate insulating film 117 of SiO₂ with thickness 100 nm isformed. SiO₂ film is formed by a PECVD using tetraethoxysilane (TEOS) asa source. Next, gate electrodes 107 and 107′ of TiW with thickness 50 nmare formed using a sputtering and then patterned with prescribedpatterns. Simultaneously to this process, a scan line 106 and an uppercapacitor electrode 108 are patterned. Next, ions of P are injected intothe patterned p-Si from the top of a gate insulating film 117 using anion implantation. Here, the ions of P are not injected to the regionwhere the gate electrodes 107 and 107′ are formed. Thereby, activelayers 103 and 103′ are completed.

Next, the glass substrate 116 is activated in an inert atmosphere (N₂)by heating so that the doping can be effectively carried out. On theglass substrate 116, a 1st insulating interlayer 118 of silicon nitride(SiN_(x)) with thickness 200 nm is formed.

Next, contact holes are formed in the gate insulating film 117 and 1stinsulating interlayer 118 on upper both ends of the active layers 103and 103′. Furthermore, another contact hole is formed in the 1stinsulating interlayer 118 on the upper side of the gate electrode 107′of the 2nd TFT. On the contact hole, Al film with 500 nm is formed bysputtering. Then by photolithographic process, a signal line 109 and apower line 110 are formed. After that, a source electrode 112 and adrain electrode 113 for the 1st TFT, and a source electrode 112′ and adrain electrode 113′ for the 2nd TFT are formed.

Then, the lower capacitor electrode 105 and the signal line 109 areconnected. The source electrode 112 of the 1st TFT 101 and the uppercapacitor electrode 108, the drain electrode 113 of the 1st TFT and thegate electrode 107′ of the 2nd TFT 102, and, the drain electrode 113′ ofthe 2nd TFT and the power line 110 are connected. Finally, the uppercapacitor electrode 108 is connected to the power line 110.

A 2nd insulating interlayer 119 of SiN_(x) with thickness 500 nm isformed to cover the power line 110. A contact hole is formed on top ofthe source electrode 112′ for the 2nd TFT. On the contact hole, using asputtering, Al film with thickness 150 nm is formed and then a lowerelectrode 115 is formed by a photolithography. Next, by spin coat usinga positive type of protective film of light sensitive resin (forexample, PC452, JSR Corporation), a 3rd insulating interlayer 120 isformed and baked. Preferably, the thickness of the 3rd insulatinginterlayer 120 consisting of a positive type of protective film of lightsensitive resin (PC452) is 1 μm and is formed to cover the edge of thelower electrode 115 by about 3 μm.

The structure of the organic light-emitting element and themanufacturing method of the protective layer are the same as thosedescribed in the previous embodiment 1.

The OLED according to the embodiment 5 of the present inventioncomprises the light-emitting unit 135 consisting of the lower electrode115, organic light-emitting layer 122 and the upper electrode 125 formedonly on the flat portion of the upper capacitor electrode 108 forming acapacitance to hold a bias voltage for the TFT to drive thelight-emitting element. Therefore, by fabricating this structure,without forming a flattening layer on the light-emitting layer, there isno electric short circuit between the lower electrode 115 and upperelectrode 125, while the short circuit is usually caused by the surfaceroughness of the stack.

Having thus described several exemplary implementations of theinvention, it will be apparent that various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements, though not expresslydescribed above, are nonetheless intended and implied to be within thespirit and scope of the invention. Accordingly, the foregoing discussionis intended to be illustrative only; the invention is limited anddefined only by the following claims and equivalents thereto.

1. An actively driven organic light-emitting device comprising: aplurality of organic light-emitting elements and thin film transistorsfor driving the organic light-emitting elements; wherein each organiclight-emitting element comprises an organic light-emitting layer and anupper electrode and a lower electrode sandwiching the organiclight-emitting layer, wherein light emitted from the organiclight-emitting layer is taken out from the upper electrode, and whereinsubstantially the entire region of the organic light-emitting layer thatis sandwiched between the upper and lower electrodes is formed over apower line for the thin film transistor in each light-emitting element.2. The organic light-emitting device according to claim 1, wherein thepower line in each light-emitting element acts as a reflective layer forthe emitted light.
 3. An actively driven organic light-emitting devicecomprising: a plurality of organic light-emitting elements and thin filmtransistors (TFTs); wherein each organic light-emitting elementcomprises an organic light-emitting layer and an upper electrode and alower electrode sandwiching the organic light-emitting layer, whereinlight emitted from the organic light-emitting layer is taken out fromthe upper electrode, wherein each organic light-emitting element isconnected to a first TFT that drives the light-emitting element, thefirst TFT being connected to a second TFT that controls the first TFT,and wherein substantially the entire region of the light-emitting layerthat is sandwiched between the upper and lower electrodes is formed overan electrode of a capacitor which is connected to the first TFT or tothe second TFT.
 4. An actively driven organic light-emitting devicecomprising a plurality of pixels, each pixel comprising: an organiclight-emitting element formed of an organic light-emitting layer and anupper electrode and a lower electrode sandwiching the organiclight-emitting layer, wherein light emitted from the organiclight-emitting layer is taken out from the upper electrode; a thin filmtransistor (TFT) for driving the light-emitting element; and a capacitorwhich holds a bias voltage of the TFT, wherein substantially the entireregion of the light-emitting layer that is sandwiched between the upperand lower electrodes is formed over an electrode of the capacitor.
 5. Anactively driven organic light-emitting device comprising a plurality ofpixels, each pixel comprising: an organic light-emitting element formedof an organic light-emitting layer and an upper electrode and a lowerelectrode sandwiching the organic light-emitting layer, wherein lightemitted from the organic light-emitting layer is taken out from theupper electrode; a first thin film transistor (TFT) for driving thelight-emitting element; a second TFT for controlling the first TFT; anda capacitor which holds a signal voltage to control the first TFT or tocontrol the second TFT, wherein substantially the entire region of thelight-emitting layer that is sandwiched between the upper and lowerelectrodes is formed over an electrode of the capacitor.